Luminous tube



Jan. 3, 1933. s, 1 JOHNSON 1,893,085

LUMINOUS TUBE Filed Sept. 27, 1928 INVENTOR,

A TTORN Y6 Patented Jan. 3, 1933 UNITED STATES PATENT OFFICE STANLEY J.JOHNSON, OF CLEVELAND, OHIO, ASSIGNOR TO NEON PROCESS, INCORPORATED, OFCLEVELAND, OHIO, A CORPORATION OF OHIO LUMINOUS TUBE Application filedSeptember 27, 1928.

The present improvements, relating as indicated, to luminous tubes havemore particular regard to neon tubes such as are extensively utilizedfor display and advert1s1ng 5 purposes, due tothe ldistinctivefspectralcolor of the neon whenexcitcd by the passage of a suitable electriccurrent therethrough. One principal object of the present invention 1sto provide an electrode assembly for use in 19 such neon tubes whichwill make it possible to employ an electrode of relatively small surfacearea, much smaller than has ever been found possible, at least where theelectrode is made of commonly available metals. In

connection with such improved electrode assembly a simplified method ofevacuation is furthermore rendered possible.

To the accomplishment of the foregoing and related ends, said invention,then, con- 20 sists of the means hereinafter fully described andparticularly pointed out in the claims; the annexed drawing and thefollowing description setting forth in detail certain mechanismembodying the invention, such disclosed means constituting, however, butone of various mechanical forms in which the principle of the inventionmay be used.

In said annexed drawing Fig. 1 is a central section through the end of atypical neon tube showing one form of the present improved electrodeassembly; Fig. 2 is a similar sectional view showing a modified form ofsuch assembly; and Fig. 3 is a diagrammatic representation of such tubeillustrating one process of manufacture.

Referring to the structural features of such electrode assembly, thebody 1 of the tube is shown in the several figures of the drawing inconventional form, it being understood that such body is of suitablediameter and length, and will ordinarily be bent in the outline of aletter or ornamental design, where the tube is used for advertisingpurposes. The ends 2 of the tube are, as shown,

preferably of somewhat larger diameter than such body 1 so as to formchambers for the corresponding metallic electrodes 3. The latter areconnected with, and supported by, the lead-in wires 4 which conduct thenecessary current to said electrodes. Each of such Serial No. 308,663.

wires 4, it will be understood, is sealed vacuum-tight at the point 5where it passes through the end of the electrode chamber 2.

Referring more particularly to the electrode assembly illustrated inFig. 1, it will be noted that a cylindrical glass sheath 6 is placed soas to surround the electrode 3, the outer end of this sheath being ofreduced diameter to a permit its attachment to the end of the chamber 2adjacent the point 5 where the lead-in wire 4 passes therethrough, asjust described. The inner end of the sheath preferably extends a shortdistance beyond the corresponding, i. e., free end of the electrode andthe space between the latter and such sheath is thereupon filled in, asshown, with a suitable dielectric, such as dehydrated sodium silicate,although a number of materials of dielectric character and capable ofwithstanding a high temperature have been found satisfactory for thepurpose of filling such space, such as asbestos fiber, low densityporcelain, plaster of Paris, and plaster of Paris mixed with a smallquantity of sodium silicate. IVhere the sheath 6, as shown, extendsbeyond the end of the electrode, the filling material 7 thus placed inthe sheath will be preferably gouged out so as to leave the endof theelectrode exposed, but otherwise the latter is completely surrounded bysuch material.

In the modified form of electrode assem bly illustrated in Fig. 2 theonly difference from that just described is the omission of any sheatharound the electrode and the fill- 35 ing material 8 of the samecharacter as that employed to fill the sheath here fills the entirespace between the electrode and the chamber 2. As in the first describedconstruction such filling material, if it extends beyond the end of theelectrode, is nevertheless preferably gouged out to expose such end.

The neon tube with an electrode assembly, such as the foregoing, may beevacuated and charged with neon gas in various ways. For example, avacuum pump 10 may be connected to the tube 1 by means of a temporarysealed connection 11, in which is interposed a valve 12 and trap 13.Between the tube 1 and such valve 12 there is a branch connection 14that communicates through a chamber 15 with a reservoir 16 containlngthe gas, e. g., commercial neon, wherewith the tube is to be filled,valves 17 and 18 controlling communication between chamber 15 andconnection 14 and the reservoir 16, respectively, and a suitablepressure indicating device 19 being also provided.

The lead-in wires 4 at the respective ends of the tube 1 are connectedto the terminals of a secondary circuit of a transformer 20, whereby anelectrical current of proper character may be supplied to saidelectrode.

With the apparatus arranged as aforesald, the vacuum pump is set inoperation with the valve 12 open and the valve 17 closed. At the sametime current is supplied to the primary winding of the transfer 20 so asto set up a current flow through the secondary coil of said transformerand the circuit including the wires l and the electrodes 3, withresultant; ionization of the atmosphere within the tube 1. Thiselectrical excitation of the atmosphere within the tube 1, it will beunderstood, takes place while the latter is in a partlally evacuatedstate, and, due to the current flow, heat is generated within said tube,which vaporizes any moisture present in such atmosphere and the vaporsare drawn ofi by the pump. When a suitable heat has been attained theelectric current is shut off and evacuation continued until the tubecools and the pressure within the latter has been reduced so far aspossible by means of the pump. Thereupon the valve 12 is closed and gasfrom chamber 15, which has previously been filled from the reservoir 16,is admitted to the tube 1 until the desired pressure of as is obtainedtherein, approximately dou 1e that which is employed in normal serviceof the tube.- When this stage is reached chamber 15 is cut oif andelectric current again turned on to excite the gas within the tube toluminosity. The tube is now a second-time evacuated until the pressureis reduced to desired operating range within the tube and the connection11 thereupon sealed off. After a brief period of aging the tube is thenready for commercial service.

Instead of the foregoing, the customary method of utilizing previouslypurified neon gas to fill the tube may be employed in conjunction with astandard mercury vapor condensation pump, liquid air traps and gaspurification systems, a method with which the art is familiar.

Also a simpler method of evacuation is possible with the presentimproved electrode, the purification system, traps, condensation pumpand the use. of liquid air being eliminated, only a rotary oil pumpbeing required for evacuation of the tube before filling the latter withneon gas in its commercial state. According to this method a bombardmentof the electrodes is caused during the process of evacuation bysupplying a suitable electriccurrent, as previously described, to thelatter, with the result that the material surrounding the electrodes isthoroughly dehydrated. A high temperature is in fact generatedthroughout the entire length of the tube being evacuated, thus assistingin the elimination of water vapor and gases which require to be removed.The tube is then allowed to cool and neon gas at a pressure of from 5 to20 mm. is allowed to enter, after which the tube is sealed off and readyfor aging.

Another method which has been successfully employed is to place thetube, when ready for evacuation, in an oven and there bake it at a hightemperature during the process of evacuation, the temperature thussupplied serving to dehydrate the material surrounding the electrodesand to eliminate water vapor and gases from the tube. The

latter is thereupon allowed to cool, after which it is filled with neongas and sealed off as before.

The dielectric mass or substance, which is preferably porous, as in thecase of dehydrated sodium silicate, that surrounds or contacts with theelectrode, in each of the two forms of electrode assembly hereinbeforedescribed, in the first place acts as a cooling agent for the electrodeand so serves to prevent excessive vaporization of the latter. At thesame time the materials named either have the inherent quality, or areeffective because the mass is porous, to absorb and segregate thegaseous impurities in the tube and in commercial neon gas, thus allowingthe neon gas to give forth its characteristic luminous qualities. Suchmaterial may absorb neon as well as so-called impurities, but shouldpreferentially absorb the latter.

. As a result of the foregoing I have found it possible to employelectrodes of much smaller area than has heretofore been consideredpossible with like conditions of pressure obtaining in the tube. Inparticular, successfully operating tubes are possible in which theelectrode has an area substantially less than-1.5 square decimeters perampere of current employed in illuminating the tube,

and after several months continuous operation such tubes do not show anyconsequential amount of vaporization of the electrode. Any of the metalsknown to be available for use as electrodes in luminous tubes, and:slpecifically neon tubes, may be employed, but

preferably use iron or tungsten.

While reference has hereinbefore been made specifically to neon tubes,it'will be understood that my improvements may be advantageously used inluminous tubes filled with other gas or gases, and particularly withneon admixed with another gas or vapor, e. g. mercury vapor, or with amixture of neon, argon and helium.

Other modes of applying the principle of my invention may be employedinstead of the one explained, change being made as regards the mechanismherein disclosed, provided the means stated by any of the followingclaims or the equivalent of such stated means be employed.

I therefore particularly point out and distinctly claim as myinvention 1. An illuminating device of the character described,comprising a glass tube, an electrode supported within said tube inspaced relation to the wall thereof, and a body of dehydrated silicatelaterally surrounding and contacting with said electrode.

2. An illuminating device of the character described, comprising a glasstube, an electrode supported within said tube in spaced relation to thewall thereof, and a body of dehydrated sodium silicate laterallysurrounding and contacting with said electrode. 3. An illuminatingdevice of the character described, comprising a glass tube, an electrodesupported within said tube in spaced relation to the wall thereof, asupplemental glass sheath within said tube laterally surrounding butspaced from said electrode, and

a body of dehydrated silicate held in said sheath about said electrode.

4. An illuminating device of the character described, comprising a glasstube, an electrode supported within said tube in spaced relation to thewall thereof, a supplemental glass sheath within said tube laterallysurrounding but spaced from said electrode, and a body of dehydratedsodium silicate held in said sheath about said electrode.

5. An illuminating device of the character described, comprising a glasstube, an elec- 10 trode supported within said tube in spaced relationtothe wall thereof, and dielectric means of greater thickness than theelectrode for preferentially absorbing impurities, said meanssurrounding said electrode and prel5 senting a divergent crater.

6. An illuminating device of the character described, comprising a glasstube, an electrode supported within said tube in spaced relation to thewall thereof, and dielectric means for conducting heat away from saidelectrode and for preferentially absorbing impurities, said meanssurrounding said electrode and presenting a divergent crater.

7. An illuminating device of the character described, comprising a glasstube, an iron electrode supported within said tube in spaced relation tothe wall thereof, and a body of dehydrated silicate laterallysurrounding and contacting with said electrode.

Signed by me, this 24 day of September,

STANLEY J. JOHNSON.

